This invention relates to signal processing techniques and circuits which remove an unwanted segment from a signal and it has particular application to deriving such a signal for driving servo-mechanisms where the unprocessed signal contains undesirable portions. It is particularly useful for signals in which the desired portion of the signal contains a leg of relatively mild slope and a rapid leg of relatively large opposite slope This circuit has particular application to deriving useful velocity formation from the "tri-phase servo patterns" as described in U.S. patent application Ser. No. 932,814 (which is still pending) which is a continuation in part of U.S. patent application No. 800,019 (now abandoned). The disclosure of these cases is incorporated herein by this reference.
This specification assumes some familiarity with the construction of magnetic disk drive data storage systems and means for generating and using servo information from coded information on the disk media but its teachings can be applied to analogous art as well.
In the specific which this invention was developed, removing unwanted signal portions and differentiating this signal with respect to a reference voltage provides a continuously accurate, useable, linear velocity signal corresponding to the radial speed and direction of the servo reading head (which provides the original input for this signal). Where this reading head is mechanically (or otherwise) linked to other heads traveling over data disks the information is directly indicative of their radial speed also.
An example of a system for generating a continuous servo signal is printed in U.S. Pat. No. 4,130,786 issued to Jacques (and incorporated herein by this reference). The Jacques' patent uses two-phase signals to generate a saw-tooth waveform and adds this saw-tooth waveform with a staircase waveform also generated by reference to the two-phase signal The result is a continuous slope linear signal.
It has also been known to charge a capacitor in a circuit and employ the discharge to smooth a signal, as for example in U.S. Pat. No. 4,584,559, issued to Penny and incorporated herein by reference. Penny does not provide for differentiation of the input signal. In addition, the Penny circuit contains offset errors contributed by two op amps (mainly from 56 and 52 with minor contribution from 48). The present invention only contains offset errors contributed by one op amp (U1-A, with minimum contribution from U1-B).